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Speakers.

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Unread postAuthor: Crna Legija » Sat Aug 20, 2011 10:59 pm

Fnord wrote:
buy one of the small amplifier kit from electronics stores like radio shack.

Radio shack still sells kits for stuff?!?



idk i'm from Australia, just guessing
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Unread postAuthor: Alster370 » Sun Aug 21, 2011 3:47 am

Car speakers use an awful lot of power, that fair in particular peak at 400w which is nearly the same amount of power from your average car battery. To run these as well you would need a car stereo to get any amount of volume from them which again drains more power.

Heres a project I did about a year ago:
Image

This wasn't a particular big boom box and that wasn't the major problem with It, It was weight. It weighed in a 8kg which isn't particularly nice to carry for any amount of distance. The battery life wasn't too good either even with a 7Amp battery you would be lucky to get 3 hours out of this thing at a medium volume. It was very loud however, as when I took it into my school and played it at full volume on the football courts, I was told It could be heard from over 100 yards away pretty easily. Price is also an issue, this cost me around £130. Was it worth it? Not really if im honest. I made it because I wanted something that wasn't available commercially at the time when I built it. The truth remains though that you will most likely not be able to make a better substitute than the portable docks currently on the market.

If you still want to make one I suggest you take ideas from existing docks like I did. A good quality Amplifier circuit is a must, try to get one with a high line output, this will give you the volume you want. cheaper guitar amplifiers are good for this but make sure you pick one with an mp3 input and one of small size, as then its more likely it will accept 12v DC.
Next, don't use a lead acid battery, no matter how small and lightweight. D or C size batteries hold alot more current for their size and weight. You could also consider a cheap li po battery pack. Finally get midranges no bigger than say 2". Its really not needed and no matter how big you go you wont get the same bass as you would do with a sub half the size. A good idea would be to salvage the speakers and sub from a cheap 2.1 speaker set for a computer.

hope this helped. :D
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Unread postAuthor: Labtecpower » Sun Aug 21, 2011 4:18 am

A friend made a boombox out of a 2*40 watt car amplifier. The thing draws about 1 amp of current.

The sound quality isn't extremely good, but enough to have fun.
It can play music for about 24 hours without changing the battery. We use a sealed lead-acid battery.

The setup cost him about 30 euro's in total.
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Unread postAuthor: Technician1002 » Sun Aug 21, 2011 9:59 am

I find the way they rate amplifiers is designed to decieve. The 2X40 watt amp is listed at putting out 80 watts total, but only draws about 12. :D I like to know that the amp's real power is as measured in RMS watts out per channel with both channels driven. That way you can compare apples to apples, instead of some vague standard such as max peak power total.
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Unread postAuthor: starman » Sun Aug 21, 2011 10:43 am

Yes I do. I build them for my audio and sound business. You'll need speakers, a stereo amp and a power supply, some interconnecting cables and some patience.

Here's a good place to start for a modern class D (digital) amp, 2 watts - 100 watts your choice. Can drive 4 ohm car speakers in good shape.

http://www.parts-express.com/wizards/se ... re+class+d

The 2 x 25W model should serve you well for this project and is only $26. There is a little video tutorial on this page to help you get started.

http://www.parts-express.com/pe/showdet ... er=320-304

An associated power supply. These amps run off of 24 VDC.

http://www.parts-express.com/pe/showdet ... er=320-316

And speakers of your choice. For what you're doing, self contained car speakers will work just fine. However, I would run to the local car stereo shop and carefully listen to some and purchase based on what sounds good and what you can afford.

Plan to build a closed enclosure to fit the speakers and amp/power supply setup....something similar to alster370's setup above would work great. Be sure to separate the 2 speakers in their own space. Tack some insulation around the inside of each enclosure. Foam rubber carpet padding works great for this.
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Unread postAuthor: starman » Sun Aug 21, 2011 11:22 am

I know, double post but different subject.

Technician1002 wrote:I find the way they rate amplifiers is designed to decieve. The 2X40 watt amp is listed at putting out 80 watts total, but only draws about 12. :D I like to know that the amp's real power is as measured in RMS watts out per channel with both channels driven. That way you can compare apples to apples, instead of some vague standard such as max peak power total.


One thing to note about amplifier power. To achieve a 3 db gain (only a modest increase) to any perceived sound pressure level, you will always have to DOUBLE to wattage of the signal to the speaker. So, if you are driving a speaker at 80 db using 1 watt of power, you will have to increase it to 2 watts to increase to output to 83 db, then go to 4 watts to increase to 86db! And here's the kicker, if you were driving a speaker at 80db with 10 watts of power (really inefficient) it would take 20 watts to increase the level to 83 db. It's all relative.

Even with efficient speakers, doubling power only ever gains you 3 db of sound pressure level....amazing huhh. And this holds true for really high watts amps. If I'm pushing 500 watts into my subwoofers to get 110 db, going to 1000 watts would only move me to 113 db. Same would hold true if I were pushing 5000 watts.....10000 watts gets me only 3 more db!!

Truth be known, most consumer speakers average 85 - 95 db per watt of input efficiency. The pro stuff moves up to the upper 90s and well over 100 db per watt in some cases. So when you are listening at normal comfortable levels you are typically using waaaaayy less than a watt of amp power.

When I refer to increasing power, you are really just increasing the voltage level (and thus the current level) of the signal to the speaker. It's just easier to relate power levels since that's the terminology typically used in audio.
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Last edited by starman on Sun Aug 21, 2011 12:14 pm, edited 4 times in total.
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Unread postAuthor: warhead052 » Sun Aug 21, 2011 11:23 am

Ok. Thanks for your help guys! I will see about actually doing this project rather then letting it sit aside for a couple years then doing it.
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Unread postAuthor: Technician1002 » Sun Aug 21, 2011 12:08 pm

starman wrote:Here's a good place to start for a modern class D (digital) amp, 2 watts - 100 watts your choice. Can drive 4 ohm car speakers in good shape.

The 2 x 25W model should serve you well for this project and is only $26.


In the ratings game, that amp is listed as a 2X25 watt model. They were kind enough to provide the conditions at which the measurement is made. That is only a 5 watt amp with distortion below 0.08% into 8 ohms or 10 watt into 4 ohms. The higher values is with 10% distortion. Many amps are power rated at high distortion levels to inflate the wattage number for advertising. Due to this some of my 25 watt amps (RMS with distortion below 0.01%) are higher power than many 250 watt amps.

Class D amplifiers are often incorrectly called a Digital amp. They are not. Due to the PWM modulation, most of the Class D amps do not have a very flat frequency response. I tend to limit my use of those amps to low frequency subwoofer drivers. For clear highs, a good class AB amp is recommended. The amp listed above is 20hz-20Khz +- 3DB. Most stuff I work with is flat +- 0.1DB. Like a switch mode power supply, there is noise associated with that operational mode that needs heavy filtering to remove. This results in filtering the high frequency response with it. For most MP3's, you should not notice much difference.

http://en.wikipedia.org/wiki/Class-D_amplifier

The big advantage to Class D amplifiers is efficiency, not Fidelity. For battery operation, the trade off is highly recommended. For studio use, you need the fidelity.
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Unread postAuthor: warhead052 » Sun Aug 21, 2011 12:33 pm

Tech, here is an idea I just got. Say I were to buy a cheapo mp3 speaker system, and then simply replace the speakers in it with the 6x9's, would it work? Or would I still need the amp?
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Unread postAuthor: starman » Sun Aug 21, 2011 12:41 pm

Those 2 x 25w will be more than enough for what he's doing. He's not going down an audiophile trail with this project. He can always go with the 100w model for $20 more if he so desires.

I too was skeptical as an old class AB man but Class D amps are now the high end of the high end in the pro sound world. I didn't class them as digital, the industry did. They do actually use high speed switching technology to gain an almost theoritical 100% efficiency, 90% in real use though. That means low heat output and light weight.

These designs have been around for some time but just recently became viable in high end applications because of the precision computer electronics of modern times. They would be impossible to implement without it.

Here's Crown's Class D entries:

http://www.crownaudio.com/amp_htm/xls_drivecore.htm

Crown doesn't position these as their high end. These are very affordable weekend warrior models. They absolutely rock...extremely clean. I use the 1000 model in my studio to drive monitor speakers.

Now check out THESE bad boys, Powersoft:

Image

http://www.powersoft-audio.com/en/produ ... eries.html

The flagship K20 is an 18,000 (yes believe it) watts bridged into 4 ohms monster all in a 1 U rack space. This is the present state of the art in tour grade amplification...and they sound like the voice of God himself through equally serious speaker systems.
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Last edited by starman on Sun Aug 21, 2011 9:10 pm, edited 7 times in total.
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Unread postAuthor: warhead052 » Sun Aug 21, 2011 12:44 pm

Remember this, I don't want to spend more than I really need to. This project is more of a "lets see if I can really do it" and a "practice" project so I can get better with soldering and electrical.
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Unread postAuthor: starman » Sun Aug 21, 2011 12:52 pm

warhead052 wrote:Remember this, I don't want to spend more than I really need to. This project is more of a "lets see if I can really do it" and a "practice" project so I can get better with soldering and electrical.


Sorry for all the theoriticals here. Car speakers are typically 4 ohms and will probably overload and just shutdown the little mp3 speaker system you were talking about so I wouldn't waste the money on doing that. If you want that big sound you were talking about, you're going to have to step it up a bit. Otherwise, you could just go with a set of computer speakers, already designed for what you are talking about.
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Last edited by starman on Sun Aug 21, 2011 8:50 pm, edited 1 time in total.
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Unread postAuthor: warhead052 » Sun Aug 21, 2011 12:56 pm

Ok. Well I will see about the amps and stuff. It depends on how willing my parents are going to be to let me do this.
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Unread postAuthor: Mr.Tallahassee » Sun Aug 21, 2011 3:28 pm

It's not hard to build an amplifier from an LM4780 IC. Ive built a couple small LM386 circuits that sound good. Here is the datasheet. You can build the circuit from the given ones on several pages.
EDIT: New note. I found that the .pdf file has the PCB printouts that can be used to etch copper clad boards to create the amplifier. It's on page 23 and it is a stereo amplifier.
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Unread postAuthor: Technician1002 » Sun Aug 21, 2011 7:28 pm

Those 2 x 25w will be more than enough for what he's doing.


I think I mentioned they would be fine for an MP3 player amp.
For battery operation, the trade off is highly recommended.
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